Superhydrophobic surfaces having a water contact angle greater than 150° and a water slip-off angle less than 10° can have many potential applications, such as from small non-wetting micro/nanoelectronics to large self-cleaning industrial equipment.
Numerous methods and materials have been developed to fabricate superhydrophobic surfaces. For practical applications, such surfaces should exhibit mechanical and chemical stability as well as abrasion resistance. For example, if a superhydrophobic surface is touched by a bare hand, the touched area of the surface could be contaminated by salt and oil and therefore could have an increased surface energy, which reduces the surface hydrophobicity. In addition, the force exerted by touching could damage the fragile rough structure of the surface, which could result in permanent loss of its superhydrophobicity. However, despite ongoing efforts, most reported artificial superhydrophobic surfaces suffer from poor mechanical and/or chemical stability.
In addition to mechanical and/or chemical stability, a commercially viable superhydrophobic surface should exhibit a reliable resistance to water pressure. In practice, a static pressure could be generated by immersing a hydrophobic surface under water and a dynamic pressure could be generated by applying water droplets or water streams onto a hydrophobic surface. Recent research shows that even a lotus leaf can be wetted within one hour after immersed under water at a depth of 0.55 m (i.e., under a water pressure of about 0.78 psi).